This invention relates generally to surgically implanted delivery and drainage catheters, such as in shunt systems that drain cerebrospinal fluid from the brain ventricles and pressure sensors implanted in fluid filled spaces or within the parenchyma of tissues. More particularly, this invention relates to an improved shunt valve including outer porous anti-fouling membranes that protect movable siphon control membranes of the shunt from external mechanical pressures. The invention also provides for a means for preventing the mechanical influence of overlying tissue from affecting the accuracy of indwelling pressure sensors.
In order to relieve undesirable accumulation of body fluids it is frequently necessary to provide a shunt for controlled drainage of such fluids from one part of the body to another. Such shunts can be required in the treatment of hydrocephalus, an ailment usually afflicting infants or children in whom fluids which ought to drain away instead accumulate within the brain and thereby exert extreme pressure and skull deforming forces. Accumulated cerebrospinal fluid can be drained away from brain ventricles by a catheter connected to a tube which conducts the fluid away from the brain to be reintroduced into the patient's vasculature. However, excessive fluid flow through such a shunt system can occur due to a siphoning effect of hydrostatic pressure, such as can be created by the elevation of the proximal catheter inlet with respect to the distal catheter outlet such as when a shunted patient is upright. It is also speculated in the hydrocephalus field that ‘over drainage’ from shunt systems may also be partially caused by abrupt spikes in fluid transport through valves systems caused by physiologic events that transiently increase intra cranial pressure such as sneezing, coughing and REM sleep.
A siphon flow control valve for use in a physiological shunt system is known that limits fluid flow through a shunt system that can otherwise occur due to a siphoning effect of a differential hydrostatic pressure between a catheter inlet and a catheter outlet. The siphon flow control valve includes a molded base that defines a fluid flow pathway between an inlet and an outlet, and that provides an inner wall structure having upper and lower seating surfaces that separate the inlet from the outlet, and a pair of flexible, elastic diaphragms seated against the inner wall structure to control against unwanted flow due to the siphoning effect. However, it has been found that the flexible, elastic diaphragms that are configured on the outer surface of the valve can be forced shut, preventing adequate fluid flow, or can become distorted, allowing excess fluid flow through the siphon control device due to external mechanical tissue pressures.
An adjustable-resistance anti-siphon cerebrospinal fluid shunt is also known that has a substantially rigid housing having an outer gas-filled chamber in pressure communication with a flexible wall of an inner chamber having inlet and outlet ports for fluid flow through the inner chamber, and flow through the inner chamber can be adjusted by controlling pressure in the gas-filled chamber, but since this design is not referenced to changes in atmospheric pressure outside the housing, the fluid flow can be improperly influenced simply by normal changes in atmospheric pressure.
It would be desirable to provide an improved shunt valve for controlling the siphon effect that can occur in shunt systems that; controls the gradient of pressures between the inlet and outlet of the valve, minimizes the influence of the negative hydrostatic pressure, while providing for atmospheric pressure reference, provides for a damping effect to reduce transient spikes in flow rate, and prevents external mechanical tissue pressure from influencing the flow through the valve. The present invention meets these and other needs.